Handheld, Portable Drum Sander

ABSTRACT

A hand held drum sander is disclosed. The sander is a self-contained power driven device having a novel method of driving and supporting the sanding drum and retaining the sanding substrate. The present invention relates to a device for the finishing of irregular shape objects by using a drum sander.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for the finishing of irregular shape objects by using a hand held drum sander in general and in particular to a self contained power driven device having a novel method of driving and supporting the sanding drum and retaining the sanding substrate.

2. Description of the Prior Art

A sander is a power tool used to smooth wood and automotive or wood finishes by abrasion with sandpaper. Sanders have a means to attach the sandpaper and a mechanism to move it rapidly contained within a housing with means to handhold it or fix it to a workbench. Woodworking sanders are usually powered electrically, and those used in auto-body repair work by compressed air. There are many different types of sanders for different purposes. Multi-purpose power tools and electric drills may have sander attachments. For example, U.S. Pat. Nos. 5,678,292 and 5,957,765 to Kimbel et al. disclose a hand-held machine tool which may be used for sanding a work piece. Oscillation of the sanding tool is provided by one of several proposed oscillation devices.

Woodworking sanders include:

-   -   Belt sander (hand-held or stationary)     -   Disc sander: A disc sander is most commonly known as a         stationary machine that consists of a replaceable circular         shaped sandpaper attached to a wheel being electrically spun         around. The usually wooden work piece (although other materials         can be shaped and worked on such as plastics, metals and other         soft materials) is set on a front bench that can be adjusted to         various angles. It can be used for rough or fine sanding         depending on the sanding grit used.     -   Oscillating spindle sander: A sander mounted on a spindle that         both rotates and oscillates in and out or up and down along the         axis of the spindle. Good for sanding curves and contours that         would be difficult with hand or orbital sanding.     -   Random orbital sander     -   Orbital sander: A hand-held sander that vibrates in small         circles or “orbits.” Mostly used for fine sanding or where         little material needs to be removed.     -   Straight-line sander: A sander that vibrates in a straight line,         instead of in circles. Good for places where hand sanding is         tedious or “blocking” is required. Most are air-powered, a few         electric.     -   Detail Sander: A hand-held sander that uses a small vibrating         head with a triangular piece of sandpaper attached. Used for         sanding corners and very tight spaces. Also known as “mouse” or         “corner” sanders.     -   Stroke sander: A large production sander that uses a         hand-operated platen on a standard sanding belt to apply         pressure for large surfaces such as tabletops, doors, and         cabinets.     -   Drum sander: A large sander that uses a rotating sanding drum.         As with a planer, the operator adjusts feed rollers to feed the         wood into the machine. The sander smoothes it and sends it out         the other side. Good for finishing large surfaces. A drum sander         is a large machine used to sand wood and plastics. This piece of         equipment is used on large woodworking projects, and when         forming plastics. A drum sander is usually 29 ½ inches (0.74         meters) wide, 24½ inches (0.62 meters) long, and weighs at least         190 lbs (86 kilograms). The equipment requires at least 2 feet         (0.6 meters) clearance on all sides to ensure sufficient working         room.     -   Wide-belt sander: A large sander similar in concept to a planer,         but much larger. Uses a large sanding belt head instead of a         planer's knife cutter head, and requires air from a separate         source to tension the belts for rough sanding large surfaces or         finishing. Used mainly for manufacturing furniture and cabinets.     -   Rolling-pin style Pneumatic Drum Sander: Perfect for hand         contouring and smoothing projects that are too large to use with         a stationary sander. Simply chuck the ⅜″ spindle into a portable         electric drill, cordless drill or air powered drill for         two-handed control.

OBJECTS AND ADVANTAGES

Accordingly, several objects and advantages of my invention are that irregular shape objects can be smoothed and shaped by using a hand held drum sander. It also is in particular a self-contained power driven device having a novel method of driving and supporting the sanding drum and retaining the sanding substrate. This device will facilitate the ability of the average handyman to smooth and finish irregular shaped objects, such as table legs, gun stocks, etc., without the need to resort to laborious hand sanding that is required at present for these tasks. This device can also be used for many other finishing functions, similar to a general woodworking sander.

LIST OF REFERENCE NUMBERS

-   7 Nut -   9 End Cover -   11 Battery -   12 Trigger -   13 Grip -   14 Screw -   15 Motor Assembly -   16 Rubber Sleeve -   17 Sand Paper -   18 Right Housing -   19 Circuit Board -   20 Left Housing -   21 Rotor -   22 Stator -   23 Shaft -   24 Ball Bearings -   25 Bearing Housing -   26 Motor Sleeve

DESCRIPTION OF INVENTION

FIG. 1 is an exploded view of my invention.

FIG. 2 is an exploded view of the motor assembly.

FIG. 3 is an exploded view of the housing assembly.

FIG. 4 is an exploded view of the motor construction.

FIG. 1 shows an overall view of the “Handheld Drum Sander”. The “Handheld Drum Sander” is composed of four major assemblies. The battery 11 or power supply is a self-contained rechargeable power supply. The battery 11 plugs into a connector on the main circuit board 19 shown in FIG. 3 on Sheet 3 and provides all the power to drive the motor assembly 15. The main housing contains the mounting structure for the battery 11, motor assembly 15, grip 13, circuit board 19 and end cover 9. The two halves of the housing 18 & 20 are joined together by screws 14. These same screws 14 retain the trigger 12 and the circuit board 19. The grip 13 shown in FIG. 1 is a rubber molded cover that is mounted to the main housing 18 & 20 to relieve operator hand fatigue caused by the operation of the sander. The trigger 12 mounts into the main housing 18 & 20 and activates a switch on the main circuit board 19 when the operator depresses the trigger 12. When the operator depresses the trigger 12, the motor assembly 15 is activated and the drum rotates. The motor assembly 15 contains the prime mover element and a device for clamping and retaining the cutting tool (sand paper). FIG. 1 shows the nut 7. The nut 7 threads onto the motor assembly and when tightened compresses the rubber sleeve 16. The rubber sleeve 16 is contained on its end, opposite the nut 7 by the flange on the motor assembly 15. Therefore, the rubber sleeve 16 expanses radially when it is compressed by the nut 7. This radial expansion of the rubber sleeve 16 retains the sand paper 17 to the motor assembly 15. The rubber sleeve 16 becomes shorter in length because the nut 7 is compressing it, and this displaced volume of rubber material makes the inside diameter smaller and the outside diameter larger on the rubber sleeve 16. This swelling action of the rubber sleeve 16 clamps the sand paper 17 to the motor assembly 15.

The motor assembly 15 is a fixed shaft motor. The center shaft of the motor does not rotate, but is fixed to the right housing 18 by a press fit into a sleeve molded into the right housing 18 center bore. The motor assembly 15 is therefore constructed inside out from conventional rotating shaft motors. FIG. 4 sheet 4 shows the internal construction of the motor assembly 15. Stator 22 is pressed fit onto shaft 23, against the shoulder on the shaft 23. The stator is laminated and has wires wound in the slots of the laminations to provide a rotating field near the rotor 21 (magnetic). The attraction and repulsions of these rotating magnetic fields are the force that provides the power for the tool. The rotor 21 (magnetic) is pressed into the motor sleeve 18. This entire assembly is kept at a fixed distance and concentric to the stator 22 and shaft 23 by the ball bearings 20 that are pressed into the bearing housing 19. These ball bearings 20 support all the motor's rotating elements and carry the load put on the tool by the sanding operation.

The end cover 9 is used to support the cantilevered end of the motor assembly 15 and protect the motor assembly 15 for the user and vice versa. The screw 14 threads into the left housing 20 to retain the end cover 9. The end cover 9 is also retained by a boss molded to the left housing 20 that fits in an elongated hole in the end cover 9 and prevents it from rotating about the screw 14.

OPERATION OF INVENTION

FIG. 1 shows the tool according to the preferred embodiment of the invention. The tool comprises a handle 18 & 20 which is preferably made of plastic, with a grip 13 preferably made of rubber for the operator to hold. The operator will position the sand paper 17 against an area of the work piece he wishes to remove material from, and then depress the trigger. When the trigger is depressed, electrical energy is sent from the battery 11 to the circuit board 19 and the circuit board 19 determines the appropriate phase of the motor stator 22 to energize to start the motor assembly 15 turning. The circuit board 19 subsequently activates the approached phase of the motor assembly 15 to keep the motor running at speed. The operator applies pressure and moves the tool around the work piece to obtain the desired material removal for the work piece. When the operator releases the trigger, the motor spins to a stop and the tool will stay in the off state until the trigger is depressed again.

The operator will need to change the sand paper 17 at the appropriate time. The sand paper 17 is changed if the desired results are not being obtained with the present piece of sand paper 17. Finer or courser grit sand paper 17 my be required to complete the job. The sand paper 17 also wears and no longer yields good results after hard continuous use. To change the sand paper 17, the tool is laid on its right side, with the screw 14 and end cover 9 facing up. The screw 17 is removed and then the end cover 9 is removed. Next, the nut 7 is turned in a counter clockwise direction by placing the spanner wrench provided in the slots in the nut 7 and resisting the rotation of the motor assembly 15 with the operator's other hand. Once the nut 7 is removed, the rubber sleeve 16 will shrink down in diameter and the sand paper 17 can be freely slid off the motor assembly 15. New sand paper 17 can now be slid onto the drum and positioned. Once this is complete, the nut 7 is reinstalled and tightened. After these tasks are completed, the end cover 9 is installed over the pin boss in the left housing 20 and the conical end of the motor shaft 23. The screw 14 is then installed and tightened. The pin boss and the conical end of the motor shaft 23 together completely define the position of the end cover 9, and the screw is used to restrain the end cover 9 in this position. The end cover 9 provides an out board support for the motor shaft 23 to resist the over-tuning moments placed on the motor shaft 23 by the work load from the operator pushing the sand paper 17 into the part to be sanded.

CONCLUSIONS AND SCOPE OF INVENTION

Thus the reader will see that the Handheld, Portable Drum Sander invention provides a highly reliable, lightweight, yet economical device that allows the operator to finish irregular shaped objects and other parts.

While my above description contains many specificities, these should not be construed as limitations on the scope of the invention, rather as an exemplification of one preferred embodiment thereof. Many other variations are possible. For example, the housing 18 & 20 could be constructed for metals to add rigidity to the tool. The power source could be changed from a battery to a wall plug. The tool would not be portable, if this were done, but the resulting product cost could be reduced. The sandpaper could be retained to the drum using adhesive instead of the present clamping method. Again these efforts could lower the tools cost, but would also lower the tools versatility.

Accordingly, the scope of the invention should be determined not by the embodiment illustrated, but by the appended claims and their legal equivalents. 

1. A sanding device to finish irregular shaped objects or the like comprising: A sanding drum directly driven by a motor inside the sanding drum, controller by a circuit board, that is powered by an enclosed battery. A method of retaining the sand paper to the motor drum using compressive nut and a concentric elastic drum that is compressed by the nut so that its diameter increases to retain the sand paper. An end cover plate used to restrain the cantilevered end of the stationary motor shaft from bending loads during operation and protect the user from the turning sand drum assembly.
 2. A sanding device as in claim 1 that is driven by an a/c line cord internal hub motor.
 3. A sanding device as in claim 1 that the sanding drum is driven by a motor in the handle of the tool and the power is transmitted to the sanding drum by a gear train or a flexible shaft.
 4. A sanding device as in claim 1 where the sand paper is retained to the sanding drum by adhesive.
 5. A sanding device as in claim 1 where the device is constructed out of metal. 